title: Altered brain morphometry in carpal tunnel syndrome is associated with median nerve pathology.
abstract: OBJECTIVE
  Carpal tunnel syndrome (CTS) is a common median nerve entrapment neuropathy characterized by pain, paresthesias, diminished peripheral nerve conduction velocity (NCV) and maladaptive functional brain neuroplasticity. We evaluated structural reorganization in brain gray (GM) and white (WM) matter and whether such plasticity is linked to altered median nerve function in CTS.
  
  
  METHODS
  We performed NCV testing, T1-weighted structural MRI, and diffusion tensor imaging (DTI) in 28 CTS and 28 age-matched healthy controls (HC). Voxel-based morphometry (VBM) contrasted regional GM volume for CTS versus HC. Significant clusters were correlated with clinical metrics and served as seeds to define associated WM tracts using DTI data and probabilistic tractography. Within these WM tracts, fractional anisotropy (FA), axial (AD) and radial (RD) diffusivity were evaluated for group differences and correlations with clinical metrics.
  
  
  RESULTS
  For CTS subjects, GM volume was significantly reduced in contralesional S1 (hand-area), pulvinar and frontal pole. GM volume in contralesional S1 correlated with median NCV. NCV was also correlated with RD and was negatively correlated with FA within U-fiber cortico-cortical association tracts identified from the contralesional S1 VBM seed.
  
  
  CONCLUSIONS
  Our study identified clear morphometric changes in the CTS brain. This central morphometric change is likely secondary to peripheral nerve pathology and altered somatosensory afference. Enhanced axonal coherence and myelination within cortico-cortical tracts connecting primary somatosensory and motor areas may accompany peripheral nerve deafferentation. As structural plasticity was correlated with NCV and not symptomatology, the former may be a better determinant of appropriate clinical intervention for CTS, including surgery.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, 02129, USA ; Department of Radiology, Logan College of Chiropractic/University Programs, Chesterfield, MO, 63017, USA.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Maeda
authors.forename: Norman
authors.initials: N
authors.lastname: Kettner
authors.forename: James
authors.initials: J
authors.lastname: Sheehan
authors.forename: Jieun
authors.initials: J
authors.lastname: Kim
authors.forename: Stephen
authors.initials: S
authors.lastname: Cina
authors.forename: Cristina
authors.initials: C
authors.lastname: Malatesta
authors.forename: Jessica
authors.initials: J
authors.lastname: Gerber
authors.forename: Claire
authors.initials: C
authors.lastname: McManus
authors.forename: Pia
authors.initials: P
authors.lastname: Mezzacappa
authors.forename: Leslie R
authors.initials: LR
authors.lastname: Morse
authors.forename: Joseph
authors.initials: J
authors.lastname: Audette
authors.forename: Vitaly
authors.initials: V
authors.lastname: Napadow
keywords: axial diffusivity (AD); diffusion tensor imaging (DTI); fractional anisotropy (FA); nerve conduction velocity (NCV); radial diffusivity (RD); voxel-based morphometry (VBM)